This explains why the fish haven't died from the ammonia, but it still leaves unanswered the question of where the ammonia is coming from.

If you go to the website for API and read the quite good information [here's the link: http://cms.marsfishcare.com/uploads/...y%208.1.08.pdf ] you will see that Ammo-Lock neutralizes ammonia but does not remove it. Although it is not too clear, it seems from my reading their information that this product works much the same as Prime and most other ammonia-detoxifying conditioners by changing ammonia (NH3) into ammonium (NH4+) which is basically harmless to fish and plants. However, this means that it is still there, and something has to be done to deal with it. In a planted aquarium, plants would use most of this ammonium. In non-planted aquaria, nitrosomonas bacteria convert it to nitrite which is slightly less toxic but still toxic to fish. Nitrospira bacteria then convert the nitrite into relatively harmless nitrate. Your zero readings of nitrite and nitrate suggest to me that this tank is either not cycled or is in a new cycle due to something having upset the biological equilibrium.

The other concern is that the ammonia may be coming from your tap water. You should test the tap water (without any conditioner in it) and see what it shows for ammonia.

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]